Automatic sorting of articles, such as baggage, packets and parcels and the like has in recent years become increasingly advantageous. Most national and international parcel delivery services and mail services today operate large distribution centres wherein automatic or semiautomatic sorting of parcels according to their destination is performed. Similarly, many baggage handling systems, such as for example for airports, use automatic sorting systems. An important part of such baggage handling or parcel sorting centres is a conveyor for automatically moving the articles to the desired location in the distribution centre appropriate for the given destination.
Sorting systems typically have a number of carts/article supporting units driven by a transport mechanism. An article in the form of e.g. a parcel or baggage is placed on a cart and driven round a track by the transport mechanism. When the article reaches the appropriate location for the given destination, the article is loaded off the track. Typically, the loading of the article on and off the cart is automatic, for example by moving an article supporting surface in a direction perpendicular to the conveying direction or by a tipping motion by the platform/article supporting surface supporting the article.
One such sorting system is known from WO 2004/011351, which has a number of carts moving along a track. A propulsion system for the conveyor comprises a stationary stator which has a coil assembly. In addition the carts have a reaction element comprising a plurality of permanent magnets mounted on a ferromagnetic carrier plate thereby providing magnetic fields. A controller controls the supply of electrical power to the coil assembly such that a travelling-wave magnetic field is generated which interacts with those of the permanent magnets to provide a driving force.
Another known system having a magnetic drive system is shown in U.S. Pat. No. 4,792,036. It relates to a transporting device of the conveyor belt type in which a transporting belt, on which the material to be transported can be supported, is capable of being moved along a transport path by a driving mechanism and carried using rolling bodies. The transport path is equipped with an electrical travelling-wave stator. Permanent magnets are arranged in series which interact with the transporting belt in a power-transmitting fashion and form a linear motor with the travelling-wave stator with an air-gap between the pole faces of the attracting permanent magnets and the travelling-wave stator.